Device for Measuring Rotation Accuracy and Dynamic Torque for Radial Rolling Bearing
The present invention relates to a device for measuring rotation accuracy and dynamic torque for a radial rolling bearing, specifically a device which is used to measure the rotation accuracy and dynamic torque of the radial rolling bearings installed in various kinds of rotation supports in order to make it possible to make a higher performance rotation support unit.
In radial rolling bearings such as ball bearings, roller bearings, tapered roller bearings or the like, is known that differences occur in the shapes and dimensions of the rolling bodies such as the balls, roller, tapered rollers, etc., as well as difference in the shapes of the raceways in the inner and outer races, and that non-repetitive minute displacements in the radial direction, called xe2x80x98Non-repetitive Run-outxe2x80x99 (NRRO), occur each rotation. In the case of radial bearings that are installed in the rotation supports of high-precision devices such as hard disk drives (HDD), these minute displacements have a large effect on performance.
Therefore, it is very important that rotation accuracy of a radial rolling bearing is measured, and that if it is found that this kind of NRRO exists, measures be taken to remove it in order to improve the performance of the device.
A prior art device, as disclosed in Japanese Patent Publication No. Toku Kai Hei 9-178613, for measuring the rotation accuracy of a radial rolling bearing for this objective has been known. FIGS. 6 thru 8 show the prior art device that is described in this disclosure.
What is measured by this device is a radial rolling bearing 1, specifically deep-groove type ball bearing, which comprises an inner race 2, outer race 3 and multiple rolling bodies, specifically balls 4 provided between the inner race 2 and outer race 3.
With the device for measuring rotation accuracy for a radial rolling bearing shown in FIGS. 6 thru 8, the NRRO of this radial rolling bearing 1 is obtained by measuring the displacement in the radial direction of the outer race 3 of the radial rolling bearing 1.
This kind of rotation accuracy measurement device for radial rolling bearing includes a frame 8 that comprises a top plate 5 and bottom plate 6 that connected by support posts 7 such that the top plate 5 and bottom plate 6 are parallel with each other. Of these, fastened to and supported by the bottom plate 6 is a drive unit 9 which drives and rotates the inner race 2 in the state where it is predeterminedly positioned in the radial direction.
This drive unit 9 comprises a spindle shaft 10 that is driven and rotated by a motor that is located in the vertical direction (not shown in the drawing), and a precision bearing device 11 such as a hydrostatic gas bearing which supports the spindle shaft 10 with high accuracy such that it can rotate freely and such that there is as little displacement in the radial direction as possible.
The inner race 2 fits without play around the top end of the spindle shaft 10 of this drive device 9.
On the other hand, fastened to and supported by the top plate 5 is a support device 12 by which the outer race 3 is supported, such that it does not rotate and such that it displaces freely in the radial direction, as well as that an axial load is applied to the outer race 3. The support device 12 has a cylindrical member 14 that is fastened to the section of retaining hole 13 formed in the center of the top plate 5. In order to apply this axial load, a through hole 16 is formed in the bottom section 15 of the cylindrical member 14, and a push rod 17 is inserted through this through hole 16 and has a rimmed section 18 attached on the top end thereof.
Moreover, the support device 12 has a push rod 17, a receiving plate 19 that is fitted inside the cylindrical member 14 such that it raises and lowers freely, and a compression spring 20 that is located between the top surface of the rimmed section 18 and the bottom surface of the receiving plate 19, and this spring 20 pushes the push rod 17 downward. Also, the support device 12 has a cover plate 21 that attaches to the opening on the top end of the cylindrical member 14, and a screw hole (not shown in the figure) is formed in the center of the cover plate 21, and an adjustment screw 22 is screwed into this screw hole. The axial load that is applied to the push rod 17 by the compression spring 20 can be freely adjusted by adjusting the position of the receiving plate 19 up or down by turning the adjustment screw 22.
Moreover, the support device 12 has a holder 23 formed on the bottom end thereof, and a circular concave hole 24 is formed on the bottom surface of the holder 23 to hold the outer race 3, so that it does not move and, so that there is no elastic deformation. On the top surface of the holder 23, there is a protruding section 25 that is formed such that it extends in a radial direction. Furthermore, the support device 12 has an anchoring plate 26 that is fastened on the bottom end of the push rod 17, and there is a protruding section 27 that is formed on the bottom surface of the anchoring plate 26 such that it extends in a radial direction.
A porous material 28, made from a sintered material or the like, is placed and held between the top surface of the holder 23 and the bottom surface of the anchoring plate 26, and to form a hydrostatic gas bearing 29 that allows displacement in the radial direction.
In other words, on the bottom surface of the porous material 28 there is a concave groove 30 whose width is a little larger than the width of the protruding section 25 on the top surface of the holder 23, while on the top surface of the porous material 28, there is a concave groove 31 whose width is a little larger than the width of the protruding section 27 on the bottom surface of the anchoring plate 26. Both of these grooves 30, 31 run in a radial direction in the porous material 28 such that they run perpendicular to each other.
There is an air-supply hole 32 formed in a part of the porous material 28 to allow for compressed air to be fed freely inside the porous material 28. When the rotation accuracy measurement device for radial rolling bearing is operating, the compressed air that is fed to the inside of the porous material 28 from this air-supply hole 32 is blown onto the surfaces of the protruding sections 25, 27 from the concave grooves 30, 31 and forms a compressed air layer between the inner surfaces of the concave grooves 30, 31 and the surfaces of the protruding sections 25, 27.
In the same way, the compressed air is blown onto the bottom surface of the anchoring plate 26 from the top of the porous material 28, and onto the top surface of the holder 23 from the bottom surface of the porous material 28 to form a compressed air layer between these pairs of top and bottom surfaces.
In this state, the holder 23 is supported such that it does not come in contact with the bottom of the anchoring plate 26, that it does not rotate with respect to the anchoring plate 26, and that it displaces freely in the radial direction by a very weak force. The axial load due to the compression spring 20 is freely transmitted by way of these compressed air layers.
Furthermore, a non-contact type displacement sensor 33 is located on part of the frame 8 between the bottom surface of the top plate 5 and the top surface of the bottom plate 6 such that it faces the outer surface of the holder 23 that holds the outer race 3.
A measurement device, such as a laser Doppler vibration meter, which can measure the minute displacement of the outer surface of the holder 23 that holds the measured object, namely the outer race 3, without coming in contact with it, is used for this displacement sensor 33. In the example shown in the figure, only one displacement sensor 33 of this kind is used, however it is also possible to use two that are located 90 degrees from each other in the circumferential direction.
When measuring the NRRO of a radial rolling bearing with the conventional rotation accuracy measurement device for a radial rolling bearing, constructed as described above, the inner race 2 fastened to the top end of the spindle 10 of the drive unit 9 is rotated by rotating the spindle 10.
Moreover, an axial load is applied to the outer race 3 by the compression spring 20 that is installed inside the support device 12, and displacement in the radial direction of the outer race 3 is measured by the displacement sensor 33.
Since the outer race 3 is supported by the hydrostatic gas bearing that is installed inside the support device 12 so that there is smooth displacement in the radial direction, the outer race 3 displaces in the radial direction just by the amount of the distortion of the rolling bodies 4 when a force in the radial direction is applied to the outer race 3 due to the aforementioned distortion. In other words, since the resistance that acts in the direction that opposes displacement of the outer race 3 in the radial direction is very small, the aforementioned distortion is nearly the same as the displacement in the radial direction of the outer race 3. Also, this displacement is detected by the displacement sensor 33.
In the case of the conventional construction shown in FIGS. 6 thru 8, it is possible to accurately measure the NRRO of the radial rolling bearing 1, however, it is not possible to measure the dynamic torque of this radial rolling bearing 1. For example, in the case of a radial rolling bearing, specifically small-diameter ball bearing or miniature bearing, that is assembled in a spindle motor for a magnetic disk drive such as a hard disk drive (HDD), in order to eliminate read and write errors, it is necessary to keep the NRRO at a minimum, as well as lower the dynamic torque in order to reduce power consumption.
Particularly, in the process of this invention described later, it was found that there is a relationship between the NRRO and dynamic torque. Conventionally, the NRRO and dynamic torque were thought to be completely separate, and that they changed independent of each other. However, from experiments through the process developing this invention, it was found that the state of the dynamic torque and increases or decreases of the NRRO are related with each other. Therefore, a device that accurately measures the NRRO of the radial rolling bearing, while at the same time measures the dynamic torque, is desired.
However in the device of the prior art shown in FIGS. 6 thru 8, it was not possible to simultaneously and accurately measure the NRRO and dynamic torque.
An object of the present invention is to provide a device for measuring rotation accuracy and dynamic torque for a radial rolling bearing to make it possible to simultaneously and accurately measure the NRRO and dynamic torque of the radial rolling bearing, and in so doing, make it possible to improve the performance of a precision radial rolling bearing assembled in a device such as a magnetic disk device.